This invention relates to cylinders for printing presses and in particular to blankets for printing cylinders.
Offset lithographic printing presses have a plate cylinder, a blanket cylinder and an impression cylinder. The cylinders are arranged with their axes parallel and with the periphery of the blanket cylinder contacting the peripheries of both the plate and impression cylinders. Ink is applied to a printing plate carried on the plate cylinder. The image is transferred from the plate to a relatively soft and yieldable elastomeric blanket of the blanket cylinder each time the plate passes the blanket cylinder. A web to be printed is passed into the nip formed by the blanket and impression cylinders to transfer the image from the blanket cylinder to the web.
The blanket cylinder usually has a leteral gap along its periphery in which the ends of the blanket are attached to a core of the cylinder. As the leading and trailing edges of the gap pass an adjacent cylinder, pressure between the blanket cylinder and the adjacent cylinder is relieved and established, respectively. The continuous relieving and establishing of pressure by the gap as the cylinders are rotated against one another causes vibration and shockloads in the cylinders and throughout the press which affect print quality. For example, at the time that the gap of the blanket cylinder relieves and establishes pressure with the plate cylinder, printing may be taking place in the nip between the blanket cylinder and the impression cylinder. Any movement of the blanket cylinder caused by the relieving and establishing of pressure at that moment can affect the image which is transferred from the blanket cylinder to the web. Also, when the gap of the offset cylinder passes the impression cylinder, any image being transferred from the plate cylinder to the blanket cylinder may be affected. The result of these vibrations and shockloads has been to limit the speed at which printing presses can be run with acceptable print quality.